Water-balance-based daily evapotranspiration estimation over the Yangtze River Basin driven by reconstructed daily GRACE/GRACE-FO TWSA (2002–2023)

Study region: Upper and middle reaches of the Yangtze River Basin (YRB), China. Study focus: This study reconstructed daily terrestrial water storage anomalies (TWSA) from 2002 to 2023 using GRACE/GRACE-FO data combined with precipitation and temperature, and estimated daily evapotranspiration (ET WB ) based on the water balance method. ET WB was compared with the Penman–Monteith–Leuning (PML) ET and Catchment Land Surface Model (CLSM) ET to evaluate its performance at different time scales and to analyze the response characteristics of water balance and energy-driven ET estimation methods. New hydrological insights for the region: ET WB inherits strong pulse signals from precipitation, introducing high-frequency noise. Low-pass filtering (Gaussian and Butterworth) significantly improves ET WB consistency with PML ET at multi-day scales, confirming its reliability for seasonal water resource assessment. In contrast, the original daily ET WB can correspond to the fast response characteristics of CLSM ET, while low-pass filtering smooths out these physically significant high-frequency signals. At the same time, there is also a phase reversal between the two. These findings indicate that ET estimation based on water balance and energy-driven have different response characteristics. The high-frequency uncertainty of the water balance method on a daily scale is a major limiting factor for accurately estimating daily evapotranspiration.